Theists having atheist friends

@fmf said
There is 2 Corinthians 6:14–15: "Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?" Although, "yoked" arguably refers to marriage.

2 Corinthians 6:14-18 isn't about marriage. It's about being "unequally yoked" with unbelievers. The question isn't in the interpretation but in its application in everyday life. To suggest it means to not have anything to do with unbelievers would mean Christians would have to leave the planet.

No, it simply means not to be involved with unbelievers in activities that are considered unchristian. To be separated from involvement in godless behavior.

The issue of Christians being married to unbelievers is covered in 1 Corinthians 7.